Technical Abstract:
Exopolysaccharide production by micro-organisms have several industrial applications in food, pharmaceuticals, or other industries. Lactic acid bacteria such as Leuconostoc mesenteroides (LM) are endemic to the environment and produce extracellular polymeric glucans such as dextran. Dextrans cause significant problems in sugar refineries where they grow as biofilms that can clog filters and inhibit sugar crystallization. The authors recently showed that some exopolysaccharide coatings inhibited corrosion on steel even when thoroughly hydrated. The polarization resistance was measured by two independent methods. Corrosion current was determined by creating a Tafel plot of the polarization curves. Both anodic and cathodic reactions are reduced by the exopolysaccharide coating. Both corrosion rate and Rp was determined for over 2 dozen strains of LM. Measured by FT-IR, complete hydration of a typical, 50 nm thick, hydrogel coating occurred within 3 minutes without loss of corrosion inhibition. The observed hydration/dehydration phenomena suggested that the film swelled so the nanoscale films were examined by AFM. When exopolysaccharide coatings were scratched, the metal substrate was exposed. The sample was then sprayed with water and allowed to equilibrate and then was re-examined by AFM. The hydrated exopolysaccharide coating flowed into the scratch and partially resealed the metal substrate. This suggest applications as a paint component or undercoat. Extensive electrochemical analyses showed that LM strain-specific exopolysaccharide hydrogels adhered to metal substrates, provided active resistance to corrosive environments, and displayed limited self-healing behavior. The authors hypothesized that polymer mobility, as well as diffusion properties, played a role in ion mobility through the nanoscale hydrogels and thus affected the corrosion inhibition. The hydrogels are bio-based, environmentally benign, and cost comparative to existing measures.